Digital code selector unit



May 30, 1967' J. 5. BURTON ETAL DIGITAL CODE SELECTOR UNIT Filed April 10, 1964 FIG. 1.

2 Sheets sheet 1 DRUM HY H f-6 RELAYS PROGRAMMER TAPE READER MANUAL 5 DECODING 9 IMMOBIL- IZER , .T mm. M V L ma A United States Patent 3,323,121 DIGITAL CODE SELECTOR UNIT John S. Burton and Everett L. Penn, Los Angeles, Calif., assignors to Monitron Manufacturing Corp., Los Angeles, Calif, a corporation of California Filed Apr. 10, 1964, Ser. No. 358,735

13 Claims. (Cl. 340-347) Our invention relates to a unit for displaying a alphanumeric symbol from information which is in the form of a digital code.

In the art of exhibiting alpha-numeric information to a large group of persons by means of a large bank of selectively excitable lamps the need for simplicity and versatility exists. This application is an improvement over the apparatus of the prior application of John S. Burton entitled, Digital Code Alpha-Numeric Indicator, filed Mar. 26, 1963, Ser. No. 268,206, now Patent No. 3,178,- 699, granted Apr. 13, 1965, which patent may be referred to for further information in this art.

In the present invention a group of memory relays stores electrically represented digital information which is to be exhibited upon a lamp bank unit having plural lamps suited to selectively reproduce a letter of the alphabet or a numeral. A similar group of motor-controlling relays is also provided, such relays being hereinafter identified as decoding relays decoding of the digital information to a specific mechanical position of a rotatable code drum is accomplished through the use of these relays. The rotatable code drum has disposed on the periphery thereof the same plurality of series of contacts, electrically interconnected, as memory or decoding relays and the same plurality of stationary contacts contacting each said series of contacts.

A motor is provided to rotate the drum, along with means to immobilize the motor. The decoding relay contacts are all connected in parallel and as a parallel group are connected in series with the coil of an immobilizing relay. The arm contact of the relay connects to the junction' between first and second field windings of the two phase motor which rotates the drum. In the actuated position, one fixed contact of the immobilizing relay shorts a rectifier-filter. In the non actuated position another fixed contact shorts the second field coil. The rectifier-filter, now being unshorted, passes a direct current through the first field coil. This two-fold modification of the fieldstructure connections of the motor producesa magnetic detent action, which immobilizes the armature of the motor in a very small fraction of a second.

The wiring of the memory relays, the decoding relays and the relation between the series of contacts onthe rotatable drum and the stationary contacts thereof is such that when the digital code established by connections between the drum and itsstationary contacts is the same as the digital code stored in the memory relays, all of the decoding relay contacts open, Prior to this occurrence at least one of the decoding relay contacts areclosed and so the motor continues to rotate the drum. When all of the decoding relay contacts open the immobilizing relay is de-energized and themagnetic detent condition immediately stops the motor and hence the rotation'of the drum.

By means of a center-tapped resistor across each of the coils of the decoding relays and a common connection from the center taps of each to one side of the contacts on each decoding relay it is possible'to operate our device without employing two-coil relays, as have heretofore been required.

By providing diodes in the digital data input lines of each display unit, all of the inputs for one digit may be connected in parallel between the source of digital information and the several display units normally em- 'ice ployed to spell out a word or sentence. Separate return circuits are provided for each display unit and only that unit being selectively provided with the return circuit, as through a stepping switch, will be actuated by the incoming digital data.

An object of our invention is to provide analog rotational positioning of an element according to digital information.

Another object is to provide a unit suited to display alpha-numeric symbol from corresponding digital information.

Another object is to provide a mechano-electric unit that is rapidin operation and which includes electro-magnetic braking means.

Another object is to provide circuitry for a said unit in which single-coil rather than double-coil relays are employed.

Another object is to provide that arrangement of conductive area for decoding upon a contact drum such that the number of interruptions of contact around the periphery with stationary contacts is a minimum.

Another object is to provide a digital code selector unit which may be connected in parallel with other like units to a source of digital information.

Another object is to provide a digital code selector unit which is relatively simple and inexpensive to manufacture.

Other objects will become apparent upon reading the following detailed specification and upon examining the accompanying drawings, in which are set forth by way of illustration and example-certain embodiments of our invention.

FIG. 1 shows a block diagram of our apparatus,

FIG. 2 shows the schematic diagram for the code positioning portion of the apparatus,

FIG. 3 shows the drum and the schematic diagram for the lamp contacting portion of the apparatus, and

FIG. 4 shows a developed pattern for the electrically conductive contact portion of the drum, including both digital positioning and lamp energizing portions.

In FIG. 1 numeral 1 represents a tape reader of the digital type. This may be the known paper tape reader having 6 bits across the tape, the bits being represented by the presence or the absence of holes punched through the paper. The reader provides corresponding electrical pulses over six parallel wires, with the presence or the absence of a pulse determined by whether or not the readercontacts meet through a holein the paper tape. The

6 bits form a character in the digital code. Reader 1 may be suited instead to read magnetic tape or punched cards, if desired.

Block 2 represents a manual programmer. This may he a keyboard with a relatively large number of keys; one for each letter, numeral and punctuation mark. Each such key closes a switch bank of six switches in the selective manner required to give an electrical connection or an open circuit for each electrical conductor according to theparticular digital code employed. We have employed thesix line modified Friden SPS Flexowriter code.

Switch 3 allows either programming source 1 or 2 to be connected to succeeding apparatus. While not so shown in the block diagram of FIG. 1, switch 3 has six arms and six sets of contacts for each of the two positions shown in each digital incoming conductor by the closed or the open position of the contacts in each instance until this information is utilized by succeeding apparatus. After this the relays are cleared and new digital information is entered. Circuit details are given in FIG. 2.

Memory relays 4 are connected to actuate the same plurality of decoding relays; block 5 in FIG. 1. Six such connections 6 are shown between the two blocks as illustrative, The decoding relays act as a group to effect stop and go control of the motor which drives the digital code drum.

An immobilizer element 9 is connected between decod ing relays 5 and motor 8. This does not require six connections, as before, but essentially only two; a going and a return circuit, When any of the plural decoding relays are closed the immobilizer is inactive and the motor turns drum 7. When all of the decode relays are open, signifying a correspondence between the digital pattern of contacts on the drum and the digital information stored in memory relays 4, the immobilizer operates to immediately magnetically lock the motor armature.

The motor is caused to stop in any one of plural magnetically detented positions, say 12. A greater number of stop positions for code drum 7 is desirable, say 48. This is accomplished by employing a four to one gear reduction drive between motor 8 and drum 7. This drive is shown schematically in FIG. 1 by the dashed line between these two elements.

Drum 7 has a plurality of series of circumferentially disposed electrical contacts 10, each series being arranged side by side as shown in the developed (unwound planar) view of the same in FIG. 4. In FIG. 1 the contacts have been shown as radially raised surfaces so that they could be seen in the figure. In practice this amount of raise may be only a few thousandths of an inch, or the contacts may be substantially level with the insulating surface of the drum.

A series of six drum digital conductive area contacts and one fully circumferential common return contact are provided for coaction with the decoding relays in the con-' trol of the motor according to the digital code previously disclosed. Stationary contacts 11, typically seven in number and aligned circumferentially in the present illustrative embodiment, connect to the decoding relays 5.

A separate series of, say 35, drum conductive area contacts are provided for utilizing the analog positioning of the drum that is accomplished by the coaction of the elements already considered. Stationary contacts 12 are provided in the same number, 35, one to contact each series of these drum contacts in their circumferential path. A bank of lamps 14 is typically employed for exhibiting the alpha-numeric symbol to be exhibited selectively by this one display unit. That is, to display the letter A, the letter B, the numeral 3, etc., etc., as desired. Thirty-five conductors, generically identified by numeral 15 in FIG. 1, connect each stationary contact 12 to one lamp. The lamps are numbered within the circles 1) through (35). A return connection is provided in common for supplying electrical energy to the lamps over the necessary two wire system, but this is not shown, being conventional.

In operation, a single digital character is formed by the presence or absence of an electrical pulse on each of the six lines passing from tape reader 1 or manual programmer 2 to memory relays 4 of FIG. 1. These set the individual memory relays accordingly, which, in turn, provide a closed circuit for the corresponding relay coils of the decoding relays if a pulse was present (a digital 1), or an open circuit if a pulse was absent (a digital 0). Then, upon an additional pulse directed to and actuating a time delay relay the circuit including decoding relays 5, immobilizer 9 and motor 8 is energized for a brief interval of time, say one second, and at the same time ing open or closed positions according to the incoming digital information, motor 8 revolving drum 7 (unless a previously exhibited alpha-numeric symbol is being repeated") and the decoding relay contacts all opening when the digital information from the memory relays matches the pattern of contacts on drum 7. This causes the immobilizer relay 9 to stop the motor and the immobilizer as a whole to detent the rotor to immobility. The drum is positioned within one second in typical embodiments of our invention. The common return connection to all lamps 14 is again closed at the end of this one second interval and those lamps having a complete circuit through stationary contacts 12 and the drum contacts 10 involved in each case are illuminated. The corresponding symbol, A, B, 3, etc. is thus exhibited. V

In this way the lamps do not randomly flicker on and off as the code drum rotates and makes and breaks under load are not performed between contacts 10 and 12. Rather, drum 7 is stationary according to our mode of operation and the contacts are joined before the current to illuminate the lamps starts to flow. If, for a particular reason it is desirable to have the lamps (or other load) flicker during the rotation of the drum, this can be accomplished by merely omitting the one second opencircuiting means.

We now turn to the schematic diagram of the code positioning portion of the apparatus as shown in FIG. 2. Terminals 21 through 26 receive the digital input information over six parallel lines; such information having originated at tape reader 1 or manual programmer 2 in FIG. 1. Diodes 28 through 33 are provided in the conductors connecting the terminals to memory relay coils 35 through 40, respectively, and with all of the diodes connected in the same polarity; with anodes to the terminals as shown.

The diodes prevent interaction between individual display units when a number of such units are operated in parallel. This is a usual configuration; to exhibit a word, a sentence or a series of numerals. A great simplification according to this invention is thereby made possible, in that all the (six) code lines from the source of digital information may be wired in parallel to all of the display units in a desired group, such as a whole line of an exhibiting board.

Terminal 34 connects to a stepper switch, or the equivalent, one contact of the same being connected to each terminal 34 in each display unit. It is seen that this connection completes the circuits through the several pick coils 35 through 40. Thus, when digital information is read into the terminals 21 through 26 of a plurality of display units it will be effective only in the intended unit, since only in that unit will the circuit be completed through a terminal 34. Each pick (or pulse-) coil, as 35, upon which a bit 1 is impressed, has a completed circuit. This is from terminal 21, upon which an actuating pulse of say +28 volts is impressed, through diode 28 from anode to cathode, through coil 35 and returning to the 28 volt supply through terminal 34. Typically this is a direct current supply, as may be provided by a battery or an equivalent power supply.

The diodes 28 through 33 prevent unwanted paths from being completed through the coils 35 through 40 of another display unit, which unit is not provided with a proper completed circuit through its terminal 34 at the time under consideration. Such an unwanted path may be formed, in the absence of diodes, from an input terminal such as 22, through coil 36, along the common conductor that connects coil 36 to coil 37, through coil 37 and out terminal 23. However, with diodes 28 through 33 present and all connected in like polarity, .diode 30 is en countered in opposite polarity to prior diode 29 and a pulse which passed through diode 29 cannot return through diode 30. Nor can it return backwards through any of the other diodes to terminals 21 or terminals 23 through 26. Obviously, without diodes several unwanted paths exist, with diodes unwanted paths do not exist. Should the apparatus be embodied to operate on negative pulses, each of the diodes 28 through 33 would be reversed in connection into the circuit as to anode and cathode.

Two coils are provided in each memory relay; those 35 through 40 previously described, and an equivalent group 41 through 46. The latter are identified as memory (or latching) coils. In FIG. 2 a dotted line 47 labelled (MEMORY) leads from the magnetic influence of the two coils 35 and 41 to contacts 48. This signifies that these coils act upon an effective armature for the relay which actuates contacts 48. These close upon current flowing in a coil of the relay and open by known spring restoring force when current is not flowing in a coil. Each memory relay is thus formed of two coils and a set of contacts; as elements 35, 41, 48; elements 36, 42, 49; elements 37, 43, 50; etc.

At terminal 54 a voltage, say 28 volts positive, is provided from a suitable direct current source such as a battery or equivalent power supply. This is connected in common to one contact of contacts 48 through 53. The other contact in the group 48 through 53 connects, respectively, to memory coils 41 through 46; the upper terminal in each case. The lower terminal of each of coils 41 through 46 pass through a resistor labelled 55 in each case for simplicity and thence to a common terminal 56. This terminal is normally connected to the negative terminal of the voltage source described in connection with terminal 54; i.e., is connected to 28 volts. This connection is also employed for reset; that is, the connection is opened by a switch, or equivalent relay, upon the data-originating devices 1 or 2 at appropriate desired times to clear the memory relays. This opens all of the contacts 48 through 53 and prepares the memory to accept the digital equivalent of the next symbol to be exhibited.

The double-coil relays, as 35, 41, 48, may be of the sealed reed type, in which both coils surround a glass capsule containing two magnetic reeds. There is no further magnetic structure. A nominal current through the pick coil, as 35, is sufficient to pull in the relay contacts. A reduced current in the memory coil, as 41, will retain the contacts in contact. Thus, current reducing resistor 55 is placed in series with each of the memory coils, for which a resistance value of 3,900 ohms is typical for a 28 volt D.C. supply. The sealed reed type relays are preferred in our apparatus because of their fast acting time; of the order of a millisecond. This makes the whole decoding process accomplishable well within the rate at which one code station on the drum can influence the decoded relays.

The group of decoding relays have coils 57 through 62 and corresponding contacts 63 through 68. This relation is indicated for the bottom relay by dotted line 69 labelled (DECODING), which extends from coil 62 to contacts 68. These relays are also preferably of the sealed reed type, but only one coil, as 57, is required for each relay because we provide two resistors 70, 71 across each such coil. This results in an economy in the cost of parts in manufacturing. The resistors 70 and 71 are connected in series across each coil and a connection is made from the center junction between each to reset terminal 56, which is normally supplied with negative 28 volts D.C. Under these conditions a suitable resistance for each of resistors 70 and 71 is 3,300 ohms.

Each decoding relay coil, as 57, is connected to the +28 volt terminal 54 through the contacts of the corresponding memory relay, as 48. The other terminal of each decoding relay coil is connected to a stationary contact bearing upon the code drum. For coil 17 this is stationary contact 73 and the portion of the interconnected contact upon the periphery ofthe drum is represented by element 79. It will be understood that the code pattern of contacts upon the code drum are all connected together, as indicated in the schematic diagram of FIG. 2 by conductor 85. This conductor terminates at one path of contact 86, which occupies the complete circumference of the drum and thus makes constant contact with stationary contact 87. This contact connects to terminal 14, hence to +28 volts in a typical embodiment. This results in all of the digital code contacts of the drum, 79 through 84 in FIG. 2, having a potential of +28 volts.

All decoding relay contacts, 63 through 68, are connected in parallel. One of each of these contacts is connected to terminal 56 by wire 88, thus typically to -28 volts. The other of each of these contacts connects to coil 89 of the immobilize relay and therethrough to terminal 54, thus typically to +28 volts.

As before, the extent of the immobilize relay is delineated by dotted line 90, also labelled (IMMOBILIZE), and including double throw contacts 91 and 92, with arm contact 93. The arm is shown in the non-actuated position, against contact 91, in FIG. 2. This is the condition for no current flow through coil 89, which results in the motor armature 99 being electrically braked and detented.

When current flows in relay coil 89 arm 83 makes contact with contact 72. This contact connects to terminal 92 through switch 95. Terminals 94 and 96 connect to a source of alternating current as indicated by the conventional symbol between them. This may be the usual 115 volts alternating current. Switch provides for motor actuation when it is closed. This switch is normally closed for a one second interval by auxiliary contacts upon tape reader 1, etc. actuating a relay coil in association with switch 95 and a suitable delay means as has been previously pointed out.

Arm 93 connects to the junction between first field coil 97 and second field coil 98 of the two-phase motor which has armature 99. The latter revolves code drum 7, of FIG. 1, preferably through a 'four-to-one gear reduction from motor to drum, so that the drum revolves one-fourth as fast as armature 99. The end of first field coil 97 that is away from the junction connection of field coils connects to relay contact 91 and also to resistor 100 and capacitor 101 in series. The second terminal of capacitor 101 connects to the second alternating current supply terminal 96. Resistor 100 and capacitor 101 shift the phase of the alternating current through the first field and thereby provide two-phase operation of the motor from the singlephase source at terminals 94 and 96. A resistance of the order of 100 ohms is suitable for resistor 100 and a capacitance of the order of 0.2 microfarad for capacitor 101 for sixty cycle per second alternating current.

The second terminal of second field coil 98 connects directly to terminal 96. Connected across contact 92 and arm 93 are diode rectifier 102 and resistor 103 in series. The rectifier may have a rating of 200 volts peak inverse voltage and approximately one-seventh ampere currentcarrying capacity, while resistor 103 has a resistance of 1,000 ohms. Resistor 104, of 220 ohms resistance, and capacitor 105, of one microfarad, typically are connected across second field coil 98.

Rectifier 102 is employed to rectify current from the alternating source connected to terminals 94, 96, when relay arm 93 is in the position shown; i.e., in contact with contact 91. This position shorts first field 97 and gives a braking elfect upon the motor. At the same time rectifier 102 provides a direct current that flows through field 98. This provides a magnetic detent action; that is, armature 99 is locked rotationally at one of a number of specific pole positions (twelve in our practice). Resistor 103 acts as the resistive portion of a resistive-capacitative filter. Capacitor is the capacitative portion. Resistor 104 prevents capacitor 105 from being shunted directly across second field coil 98, which would otherwise bypass appreciable alternating current from that field during normal operation of the motor.

When our-display unit is in operation the following actions take place in decoding the letter A of the alphabet.

In the Flexowriter code employed as an example, the letter A is digitally represented by a 1 in channels 1 and 6 and by a O in the rest of the channels; Le, a included in channels 2, 3, 4, 5. Therefore, a pulse of electricity will appear at terminals 21 and 26 in FIG. 2 when the A is introduced and there will not be a pulse appear at any of terminals 22 through 25.

A momentary current flow through relay coils 35 and 40 because of the pulses at terminals 21 and 26. Terminal 34 is connected to the originating digital machine along with a source of electricity to complete the circuit through to terminals 21 and 26. The current through coils 35 and 40 close contacts 48 and 53. This completes a circuit through terminal 54, contacts 48, memory coil 41, resistor 55 and terminal 56, allowing current to flow from the +28 volt to the 28 volt terminals of the power supply. An equivalent circuit is completed through elements 54, 53, 46, 55 and 56. Contacts 48 and 53 remain closed because of the magnetic attraction produced by coils 41 and 46, respectively, upon these contacts. In our embodiment this memory feature is established within three milliseconds.

Since the contacts at 4-8 are closed, coil 57 of decoding relay for this channel is energized through resistor 71 and terminal 56. There is then a complete circuit between the energizing terminals 54 and 56. This closes contacts 63, which are controlled by coil 57. In a similar manner, since contacts 53 are closed, coil 62 is energized through its resistor 71 and terminal 56. This closes contacts 68.

It is seen that if any one or more of contacts 63 through 68 are closed there will be a flow of current through immobilizer relay coil 89 and that relay arm 93 will be brought in contact with contact 92, allowing the motor to run if switch 95 is closed.

Although contacts 49 through 52 are open, it will be seen that if any of the stationary contacts '74 through 77 are in contact with drum contacts 80 through 83 the corresponding decode contacts 64 through 67 will also be closed. This is because all of the drum contacts have the +28 volts from terminal 54 impressed upon them and that there is a path through each decode relay coil and the resistors in shunt thereto to the +28 volt terminal 56. For coil 58 this is through contacts 80 and 74, through coil 58 and resistor 70 (and through resistor 71 in parallel therewith) and the center-tapped connection of these resistors to terminal 56.

The same manner of completing the circuit exists for the other decoding relays if the decode pattern presents a drum contact under the represented stationary contact. In the general case, the drum 7 (FIG. 1) will not be in the decode position corresponding to letter A and that there will be drum contacts present at digital line positions corresponding to some other symbol. For instance, the letter C has drum contact closures at 79, 80, 83 and 84.

When switch 95 is closed for the one second interval, as has been brought out, armature 99 will revolve. This will bring various digital contact combinations under stationary contacts 73 through 78 and the motor armature will continue to revolve. However, when the digital pattern corresponding to the letter A comes under the stationary contacts there will be electrical continuity betweencontacts 73 and 79 and between 78 and 84, but not at contacts 7480, 75-81, 76-82, or 77-83. This condition Will cause a short across coil 57. The contacts at 48 are closed and the short circuit extends from coil 57 through contacts 48, through contacts 86, 87, through contacts 73, 79 and back to coil 57. Both terminals of coil 57 are at +28 volts and so no current can llow through it; to put it another way. Current does flow through each of resistors 70 and 71, thence to 28 volts at terminal 56,

but this current, of course, does not produce a magnetic field in the coil and so contact 63 is opened.

In exactly the same way contact 68 is also opened. It will be recalled that of the memory relays only contacts 48 and '53 have been closed, these corresponding to the memory retention of the incoming digital information for the letter A. Thus, none of the other memory contacts 49 through 52 are closed. At the circumferential position of the drum corresponding to digital A none of the drum contacts 80 through 83 are present and so there is no electrical continuity at stationary contacts 74 through 77. Decode coils 58 through 61 are thus not energized and corresponding relay contacts 64 through 67 are not closed. We have thus arrived at the condition when all of the motor-controlling contacts 63 through 68 are open. This prevents a current flow through immobilizer coil 89 and this condition brakes and magnetically detents armature 99 as has been explained. 1

Accordingly, when switch is closed for one second, to recapitulate the characteristic action, the motor is mediately energized (unless the drum is already at letter A) and armature 99 rotates for the fraction of a second required to make a part, or at most nearly all, of one revolution; seeking the digital code pattern on the 'drum corresponding to the letter A. When this is found the motor is abruptly stopped and locked by magnetic detent. The drum then remains stationary and nothing happens for the remainder of the one second interval. At the end thereof, electrical energy is supplied to the several lamps having closed circuits on the display contact portion of the drum through cor-responding stationary contacts and the unit displays the letter A in this instance. This display is held until the memory relays are cleared and new digital information is supplied, which is handled as before.

Briefly recapitulating, there are four conditions of the apparatus brought about in response to a digital bit impressed upon a memory relay in relation to the operation of the motor having armature 99:

(1) A 1 (i.e., a pulse of electricity) is impressed upon the relay coil, such as coil 35. Contacts 48 are closed. When the situation is such that a drum contact, as 79, is also closed, there is no voltage drop across the decoding relay coil, as coil 57. Each terminal thereof is at +28 volts. Thus, contacts 63, associated with coil 57, are open. Insofar as this one digital channel is concerned the motor does not rotate.

(2) A 1 pulse is impressed upon memory relay coil 35 and drum contact 79 is not closed, due to the drum being at some circumferential position other than correspondence with this bit in the digital code. There is a voltage drop of 28 volts across coil 57 and resistor 71 in series, contacts 63 are closed, immobilize coil 89 is energized and the motor rotates.

(3) A 0 (no pulse) is impressed upon memory relay coil 35, but drum contact 79 is closed. There is a voltage drop of 28 volts across coil 57 and resistor 70 in series, contacts 63 are closed, immobilize coil 89 'is energized and the motor rotates.

(4) A 0 is impressed upon memory relay coil 35 and drum contact 79 is open. There is no voltage at all at the terminals of coil 57, contacts 63 are open, coil 89 is not energized and so the motor does not rotate.

It will be understood that although the unit we have described herein performs the useful task of providing alpha-numeric display, the same digital to analog conversion (determination of specific rotational positions of a shaft and drum) can be employed to accomplish other electrical contacting or mechanical functions. Such functions include establishing contacts for connecting multielement antenna arrays in one of several possible patterns for steering the same in a desired direction for receiving purposes, or to open or close a valve to a given degree accordingto digital information supplied.

Also, broadly considered, the memory, decoding and immobilizer relays, the motor and the drum comprise a randomly selectable programming or stepping switch. Six

9 digital code lines allow selection-of forty-four drum positions at will. The entry codes, output patterns and/or stored programs can be changed by alterations of the master drawing for the printed circuits preferably employed in embodying this invention.

FIG. 3 shows the schematic diagram for the lamp contacting portion of the apparatus; i.e., that required to accomplish the selected alpha-numeric display from the digital decoding portion of the apparatus that has been described.

The lamp contacting portion is normally part of drum 7 and in practice stationary contacts 12 are aligned with contacts 11, so that the digital portion and the lamp contacting portion appear as only a single device. However, careful inspection of the drum pattern of conductive areas reveals that the digital and the lamp portions are electrically separate. This is to permit the use of low voltage DC. for the digital control and 115 volt A.C. for energizing the lamps.

A plan view of the cylindrical drum 7 is shown in FIG. 3. The view of the same in FIG. 1 is an end elevation. In FIG. 3, metallic contacts are shown hatched rather than in solid black in accordance with required drafting practice. However, these cont-acts lie around the circumference of the drum and are not in section.

It will be noted that drum 7 is broken in the central portion to indicate that there are typical 35 series of contacts, of which only six have been shown in FIG. 3 for simplification. Similarly, only seven stationary contacts 12 have been shown although this number is normally 36 for the lamp contacting portion of the drum. The top drum contact 110 completely surrounds the drum so that the stationary contact 12 at the top of the figure always makes contact with it regardless of the circumferential relation between the two. This top con-tact 12 connects to terminal 111, which is one of the terminals at which electric power is supplied to operate the lamps. The other such terminal is 112. Between the two 115 volt alternating current is normally supplied, although this may be of any nominal voltage and may be either alternating or direct current according to the requirements of the load to be energized.

Terminal 112 connects to common conductor 114, which may also be connected to a ground 115 when this would be desirable or conventional. Conductor 114 connects to one terminal of each of the lamps, as (1), (2),

(3), (33), (3'4), (35). The conductor from each other lamp terminal connects to a stationary drum contact 12 in each case. The many individual drum contacts 10 which lie in a series of such contacts in the path of a given stationary contact 12 are so disposed that when drum 7 has a particular circumferential position specific lamps in the group (1) through (35) are illuminated. For the letter A the lamps illuminated in the group 14 of FIG. 1 are typically numbers (2), (3), (4) along the top, -a vertical row (31), (26), (21), (16), (11), (6), another vertical row (35), (30), (25), (20), (10), and a cross bar (17), (18), (19).

In order that the lamps will not be energized while the drum is turning to change the alpha-numeric symbols switch 116 is provided. This is shown in the closed position, since it is closed save for the one second period when the drum does revolve. This switch is operated in concert with switch 95 of FIG. 2, as by both being sets of contacts upon one relay. Switch 116 is closed normally While switch 95 is open and switch 116 is open while switch 95 is closed for the one second period.

In the pattern of metallic contacts upon drum 7 for the lamps, as shown in FIG. 3, we prefer to allow this pattern to be arranged as other circumstances may dictate. In our typical mode of operation in this part of the apparatus current is not flowing while contacts between the drum and the stationary contacts are being made or broken. Thus, there is no wear from this factor upon the 1% drum nor upon any of the lamp circuitry associated with it.

However, with the digital pattern for selecting the drum position corresponding to the digital code for each alphanumeric symbol decoding relay coils 57 through 62 are energized with current each time a contact 79 through 84 of the drum is made. The current employed is in the milliampere range, but it is desirable to minimize the number of actuations of these relays from the standpoint of long equipment life.

Accordingly, in recognition of this need, we arrange the alpha-numeric symbols such that the digital representation of each, when combined with those adjacent around the drum, is such that the contacting areas of each path are as long as possible. This we actually accomplished by placing each digital equivalent of an alphanumeric symbol on a card and then arranging the cards as required until the order sought to give the desired result was obtained. For this reason the order upon our drum is not A, B, C, X, Y, Z, l, 2, 3, but is '(apostrophe), U, M, 6', K, S, O, A, &, (off), I, 9, Q, s R: L: a C, T: (p Z1 Y: L 7 a G, X, E, 5, N, V, D, 4, 0', 2, B, W, F.

While our discovery of this order for this code was empirical, the manner in which an order for any code has been set forth to give the desired result. The natural law involved consists in minimizing the number of changes for a given number of combinations required to be handled by the contact drum.

All of the conductive contacts on drum 7 which pertain to the digital selection are connected together so that common stationary contact 87 (FIG. 2) provides a return circuit. Similarly, but separately, all of the contacts on drum 7 which pertain to the lamp-energizing section (FIG. 3) are connected together and to path so that a common return circuit is provided for these drum conductive areas.

In order to provide low contact resistance for the drum conductive areas these areas resulting from the printed circuit processing are given a plating of nickel and thereafter a plating of rhodium. The characteristics of rhodium as to hardness to resist wear and as to good electrical conductivity in this use are known.

The stationary contacts, as 11 and 12, may be formed of work-hardened palladium alloy wire and may be of the multiple-finger type construction, with, say, three fingers to each contact. This alloy has a low contact resistance to rhodium.

Elements 4 through 12 in FIG. 1 are concerned with the control function of our unit and are preferably mounted within an enclosed housing. Printed circuit connecting conductors for the numerous connections indicated in FIG. 2 are employed in a preferred embodiment. This re- .sults in simplicity and in reliability in manufacturing.

FIG. 4 shows the conductive contact areas of the drum of FIGS. 1 and -3 in the developed (fiat, planar) form. These are shown by the hatched portions, with the clear portions corresponding to insulated non-conductive areas. The digital drum contact areas occupy the seven vertical paths at the left of the figure, while the second, or lamp, contact areas occupy the thirty-nine vertical paths at the right of the figure. There is one complete common path at the left of the digital areas, and one complete common path at both the left and the right of the second contacting areas. An all on conductive strip appears at the top of the group of second areas. The indentification of the digital and the lamp on-off pattern for each alphanumeric symbol is given at the extreme left.

It will be noted that the non-contact areas are longer (vertically) than the adjacent contact areas for the digital pattern according to our preferred arrangement.

The mutually exclusive contacting arrangement for energizing motor 8 OR second (lamp) contact areas 110, etc. is represented in FIGS. 2 and 3 by a dotted line from element 95 .and to element 116, respectively, signifying a common mechanical tie which opens one switch while it closes the other, as by an armature of a relay with double throw contacts and corresponding separate arm contacts.

Alternate embodiments include a disk or an endless tape for carrying the drum contacts. Instead of incandescent lamps, gaseous discharge lamps or portions of a fluorescent panel may be made to glow upon being excited by the two terminal circuits provided by our explicit embodiment.

Other modifications may be made in the arrangement, size, proportions and configuration of the apparatus, as well as in the details of the electrical circuits without departing from the scope of our invention.

Having thus fully described our invention, We claim:

1. A digital code selector unit having;

(a) a memory comprised of a plurality of relays to accept electrically represented digital information having a plurality of bits of information for each digital character,

(b) the same said plurality of decoding relays as comprise said memory,

(c) plural means to individually connect each one of said decoding relays to each one of said relays of said memory,

(-d) a rotatable code drum having thereon the same said plurality of series of electrically interconnected contact areas,

(e) a same said plurality of stationary contacts disposed to individually contact each of said series of contact areas,

(f) means to individually connect said plurality of said decoding relays to said plurality of said stationary contacts,

(g) means to rotate said code drum in one direction,

(h) magnetic means to immobilize said means to rotate said code drum, and

(i) means to electrically connect said means to immobilize to all said decoding relays,

( j) whereby said drum is immobilized upon the digital information stored by the relays of said memory matching the digital equivalent of the electrical connections between said series of contact areas and said stationary contacts,

(-k) to thereby open the contacts of all of said decoding relays.

2. The digital code selector unit of claim 1 in which;

(a) a second plurality of electrically interconnected series of contact areas is disposed upon said rotatable code drum electrically separate from the plurality thereof first mentioned, and

(b) a second plurality of stationary contacts is disposed to individually contact each of said second plurality of electrically interconnected series of contact areas.

3. The digital code selector of claim 2 which additionally includes;

(a) switching means having first and second mutually exclusive contacts,

(b) first means to connect said first mutually exclusive contacts to energize said means to rotate said code drum,

(c) second means to connect said second mutually exclusive contacts to energize said second plurality of contact areas upon said code drum, and

((1) means to close said first mutually exclusive contacts for a short period of time in comparison with the period of time during which said second mutually exclusive contacts are closed.

4. The digital code selector unit of claim 1 in which;

(a) said plurality of said electrically interconnected series of contact areas are arranged within the respective series to be circumferentially shorter than adjacent non-contact areas,

thereby to provide a minimum number of interruptions of electrical contact between the contact areas of 12 said series and said stationary contacts contacting the same.

5. The digital code selector of claim 1 in which said means to rotate said code drum includes;

(a) a motor having first and second field coils and an armature, and I (b) said first and second field coils are electrically connected differently for two phase operation of said motor.

6. The digital code selector of claim 5 in which said means to immobilize includes;

(a) means to short said first field coil for immobilizing said armature, and

(b) means to pass a direct current through said second field coil for immobilizing said armature at selected rotational position.

7. The digital code selector of claim 1 in which each said recoding relay includes in circuit;

(a) a relay coil,

(b) a pair of relay contacts,

(c) first and second resistors connected in series across said relay coil,

(d) a connection from one terminal of said relay coil to a said stationary contact of said drum,

(e) a connection from the other terminal of said relay coil through the contacts of a relay of said memory to one of said pair of relay contacts of each said decoding relay, and

(f) a connection from the junction between said first and second resistors to the other of said pair of relay contacts,

(g) whereby different circuits are completed depending upon whether a connection is made through a drum contact or through a contact of a relay of said memory,

8. The digital code selector of claim 7 which additionally includes;

(a) said means to immobilize has an immobilize relay with a coil and contacts, and

(b) means to connect the coil of said immobilize relay to an electrical energizing source through each of said relay contacts of each said decoding relay in parallel,

(c) whereby when said difierent circuits are completed through both a said drum contact and a contact of a relay of said memory,

(-d) said immobilize relay is not energized and said means to rotate said code drum stops.

9. The digital code selector of claim 8 in which;

(a) neither of said different circuits are completed through said drum contact or a contact of a relay of said memory,

(b) said immobilize relay is not energized, and

(c) said means to rotate said code drum stops.

10. The digital code selector of claim 8 in which;

(a) one of said different circuits is completed through only said drum contact,

(b) said immobilize relay is energized, and

(c) said means to rotate said code drum rotates.

11. The digital code selector of claim 8 in which;

(a) another of said different circuits is completed through only a contact of a relay of said memory,

(b) said immobilize relay is energized, and

(c) said means to rotate said code drum rotates.

12. The digital code selector unit of claim 1 which additionally includes;

(a) the same plurality of diodes as said plurality of relays in said memory,

(b) means to connect one said diode in series with the source of one of said bits of information and one terminal of the coil of one of said plurality of relays in said memory, and

(c) means to connect the second terminal of each said coil to a common terminal,

((1) whereby electrical pulses representing said bits of information may flow only from the source of said bit to said common terminal.

13. The digital code selector unit of claim 12 in which;

(a) each said diode is connected in the same polarity in the series connection recited as the polarity of connection of each other said diode.

References Cited UNITED STATES PATENTS 2,775,727 12/1956 Kernahan et al 340--347 2,873,439 2/1959 Lahti et al. 340-347 14 2,909,769 10/ 1959 Spa-ulding 340-347 2,989,680 6/1961 Weiser et al. 340-347 3,045,157 7/1962 Jacquet et a1 340347 OTHER REFERENCES Page 17, March 1962, Alphanumeric Display, by Kamp et al., IBM Technical Disclosure Bulletin, vol. 4, No. 10.

DARYL W. COOK, Acting Primary Examiner.

10 MAYNARD R. WILBUR, Examiner.

W. J. KOPACZ, Assistant Examiner. 

1. A DIGITAL CODE SELECTOR UNIT HAVING; (A) A MEMORY COMPRISED OF A PLURALITY OF RELAYS TO ACCEPT ELECTRICALLY REPRESENTED DIGITAL INFORMATION HAVING A PLURALITY OF BITS OF INFORMATION FOR EACH DIGITAL CHARACTER, (B) THE SAME SAID PLURALITY OF DECODING RELAYS AS COMPRISE SAID MEMORY, (C) PLURAL MEANS TO INDIVIDUALLY CONNECT EACH ONE OF SAID DECODING RELAYS TO EACH ONE OF SAID RELAYS OF SAID MEMORY, (D) A ROTATABLE CODE DRUM HAVING THEREON THE SAME SAID PLURALITY OF SESRIES OF ELECTRICALLY INTERCONNECTED CONTACT AREAS, (E) A SAME SAID PLURALITY OF STATIONARY CONTACTS DISPOSED TO INDIVIDUALLY CONTACT EACH OF SAID SERIES OF CONTACT AREAS, (F) MEANS TO INDIVIDUALLY CONNECT SAID PLURALITY OF SAID DECODING RELAYS TO SAID PLURALITY OF SAID STATIONARY 